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Thesis (M.S. - Hydrology and Water Resources)--University of Arizona, 2003. / Includes bibliographical references (leaves 285-292).

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Column leaching experiments were conducted to simulate in-situ leaching processes and to provide information on the mechanisms and extent of copper recovery, acid consumption, and chemical composition of recycled raffinate. Two 1.52-meter by 0.30-meter columns, each loaded with approximately 150 kilograms of copper oxide ore from the Florence porphyry copper deposit, were leached with a dilute sulfuric acid solution for 84 days. Computer simulation of the saturation state and aqueous mass transfer of predominant elements during the column tests was performed using EQ3NR, an aqueous solution speciation-solubility modeling code and the geochemical mass balance modeling code NETPATH. These modeling codes were used to quantify the amount of minerals dissolved and precipitated in the columns during the column leaching experiments. NETPATH mass balance models containing Cu-montmorillonite and chrysocolla as sources of copper match observations of pre-leach material. Cu-montmorillonite contributed 55% and 34% of the dissolved copper in the columns effluent.

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The groundwater level in Pinal County has been dropping steadily since large scale expansion of irrigated agriculture began in the early 1940s. The current average rate of decline of the water table of about nine feet per year means steadily increasing pumping costs. Since over 95 percent of the water in Pinal County is used by farmers, the initial impact of increasing pumping costs fall almost entirely on farmers, resulting in continuous adjustments in resource use, cropping patterns, output and income. The principal objective of this dissertation is to estimate the extent and significance of the adjustments Pinal County farmers will make over time as their water costs increase due to increasing pumping lifts. Farmer adjustments to increasing pumping costs are analyzed in two major steps. First, an economic model of typical Pinal County farms is developed for four size groups and three pumping lifts within each size class. This model provides estimates of net return over variable costs for the various field crops in Pinal County for each farm size and pumping lift. Second, data provided by the analysis of typical Pinal County farms is incorporated in a linear programming model which estimates enterprise combinations, output, and income from typical farms subject to restrictions regarding factor supplies, and assuming profitmaximization as a goal. Changes in cropping patterns, output and income over time are estimated by comparing the result from a linear programming model based on 1965 water costs to the results from a model based on projected water costs in the years 1966, 1976, 1986, 1996, and 2006. The results from this model suggest that Pinal County farmers do not face an immediate "water crisis", as often suggested. While the declining water supply will require large adjustments over time in acreage of low-valued hay and feed grain crops, this will not substantially affect net farm income because these crops provide a relatively small portion of the net income to Pinal County farmers. Cotton provides Pinal County farmers with most of their net income and the return to cotton is more dependent on lint price and Government programs and payments than on water costs. Certain assumptions regarding prices, technology and institutions are implicit in this model. Changes in these assumptions can generally be reflected by general or relative price changes. A sensitivity analysis of the effect of price changes shows that net income is very sensitive to changes which affect cotton, but not very sensitive to price changes in other crops in the model. Cotton acreage is determined by Government acreage allotments. However, price decreases in cotton do not result in decreases in cotton acreages with current Government payments, while price decreases in other crops generally result in substantial decreases in output. Pinal County farmers, like the users of any stock resource, will continue to face declining net returns as the cost of tapping the stock of water increases. Adjustments in land values, net income, and number of farms will continue. The continued overdraft of water by Pinal County farmers apparently presents no particular threat to nonagricultural water users in the foreseeable future because nonfarm consumption is small relative to the total supply. Costs of supplying the nonagricultural sector with water would increase, but would be small relative to the productivity of water in these uses.

The decline of groundwater levels in Final County, Arizona has not only resulted in land subsidence, but has entailed higher pumping costs for irrigation water. The Pinal Active Management Area (PAMA) is thus one of four critical groundwater overdraft areas in which water conservation is to be enforced by mandate of the Arizona Groundwater Management Act. The Groundwater Management Act as it relates to the PAMA is evaluated with respect to an accepted theoretical groundwater management model in order to determine its potential effectiveness in achieving basin-wide water conservation. The indications are that implementation problems may greatly reduce the effectiveness of the Act. The potential for farm-level water conservation is evaluated by performing a detailed benefit-cost analysis of four alternative on-farm water conservation measures. These include laser leveling, which improves the water application efficiency of traditional furrow irrigation systems from 60 to 85 percent, the installation of center pivot or drip irrigation systems, with potential water application efficiencies of 75 and 90 percent respectively, and the introduction of lettuce, a high-value and less water-intensive crop, into the traditional crop mix. The social and private profitability measures obtained from the analysis indicate that only cotton and lettuce show a profit in the long run with respect to all the irrigation systems, and these profits are highest when farms are laser leveled. The remaining traditional crops, namely alfalfa, wheat, barley, sorghum and safflower, all indicate losses. The magnitude of these losses is least in laser leveled farms. When crops are combined in a farming enterprise so as to simulate more realistic conditions, laser leveling yields the highest net returns to water in the long run. These results lead to the conclusion that the effectiveness of the Groundwater Management Act can be considerably enhanced by providing incentives that encourage farmers to invest in laser leveling.